How IN/OUT Whole House Water Filters Work
Simple point of entry (whole house) water filters that do not backwash to clean and resettle their filter media are often called "in/out" filters. The water simply goes in one side, passes through the filter media, then goes out the other side. There's nothing fancy about this type filter. It's a big tank called a mineral tank that is filled with granular filter media. It has a simple center tube called a "riser" to direct the flow of water inside the tank.
The filter pictured above is the most common style, the downflow. Water enters the tank head from the left, is released into the top of the tank, and works its way through the media to the bottom of the tank. At the very bottom of the tank the water passes through the fine slots in the riser basket, then is forced upward through the riser to the tank head and exits the filter at right.
The Upflow Version:
In the upflow version of the same filter, water enters the tank head and is sent down the riser tube to be released at the bottom of the tank. It slowly works its way upward through the media and is collected at the top and exits the filter.
More about In/Out Upflow Filters.